Deterioration of walking (gait) in the elderly is a significant problem contributing to loss of functional independence, impaired quality of life, falls, fear of falling, secondary disease, impairment and disability. Exercise programs offer a good means to improve or maintain gait function in the elderly, however, the mixed, overall limited successes of various multimodality exercise programs point to a pressing need to identify from the myriad of exercise components that could be performed, those which target the most critical, functionally relevant age-related impairments. Numerous age-related impairments in strength, flexibility, balance, etc., exist and not surprisingly we have found numerous lower extremity biomechanical gait parameters that are reduced compared to young adults in the elderly. However, we have identified only a very few to be consistently reduced at different walking speeds, and surprisingly, only one to be consistently reduced in healthy elderly people and exaggerated in elderly people who recurrently fall: reduced peak hip extension at the end of stance. Reduced peak hip extension, in association with dynamic increases in anterior pelvic tilt (lumbar lordosis) and short step length, implies that hip extension flexibility is a critical factor to gait performance in the elderly. While hip extension flexibility has been long thought to be of functional importance by rehabilitation clinicians, it has never been rigorously explored, particularly in the elderly population, and hip extension stretching is not typically recommended as part of general exercise programs. We hypothesize that many elderly subjects will measurably benefit from hip extension stretching such that general exercise programs which include a component of hip extension stretching will be the most effective in improving gait performance. Although hip extension stretching is minimally strenuous, performing the stretch effectively requires that the person is properly educated and supervised at least for an initial time period. Also, while long-term compliance with such a minimally strenuous exercise could be good, the necessary time, investment, and commitment warrants a definitive demonstration of its effectiveness. In this project, we will (1) quantify the extent of hip extension reductions both passively and dynamically in elderly subjects compared to young adults, (2) test the hypothesis that a 10-week trial of supervised, isolated, hip extension stretching improves age-related gait parameters in both healthy and frail elderly populations and (3) apply our forward dynamic modeling expertise to fully examine the effect of this isolated biomechanical intervention which will allow us to test the hypothesis that reduced hip extension is a functionally limiting impairment rather than some unknown dynamic consequence as well as predict which persons will benefit from stretching. While the project will test if a remarkably simple, minimally strenuous, but currently unaddressed strategy can improve age-related gait changes in the elderly, the controlled nature of the project will importantly advance the mechanistic, biomechanical underpinnings necessary to develop the most effective exercise programs to improve and maintain walking function in the elderly. [unreadable] [unreadable] [unreadable]